Electromagnetic (EM) waves have been used in various applications to supply energy to objects. In the case of radio frequency (RF) radiation for example, RF energy may be supplied using a magnetron, which is typically tuned to a single frequency for supplying RF energy only in that frequency. One example of a commonly used device for supplying RF energy is a microwave oven. Typical microwave ovens supply RF energy at or about a single frequency of 2.45 GHz. Other apparatus have been used to process objects. For example, conventional ovens may be used to cook, heat, and dry objects. Other processing apparatus may be employed in fields of chemical production, products manufacturing, materials fabrication, etc. In each of these fields or apparatus, a need may exist to monitor the progress of a process or processes.